Technical Abstract:
Mosquitoes are the primary source of many diseases, including yellow fever, malaria, dengue fever, encephalitis and West Nile Virus (WNV). Because the WNV is maintained in nature by the bird-mosquito-bird cycle, identification of odors emitted from avian hosts will aid in the development of better trapping methods for the mosquitoes that transmit WNV. Therefore, we are examining novel methods of collecting these odors from chickens for the identification of candidate attractants for these mosquitoes.
Compounds from 12.5 g of chicken feathers were collected for two months on 500 mg of Anasorb-747 stored in a sealed glass container. Trapped compounds were then eluted back off of the sorbent with 2 mL of carbon disulfide. Extracts were then separated using a DB-5ms column (30m x 0.25 mm x 0.25 µm) and analyzed on a Finnigan MAT GCQ ion trap mass spectrometer. Chicken feathers (~ 60 mg) were packed in a thermal desorption tube. The tube was heated ballistically to 200°C to purge volatiles onto the head of a DB-WAXetr column (30m x 0.25 mm x 0.25 µm) where they were cryo-trapped and then analyzed on a Finnigan Trace GC/MS single quadrupole mass spectrometer (ThermoFinnigan). Compounds from both methods were ionized by EI and identified using the NIST database; when available; standards were injected and analyzed for positive identification.
Experiments using an olfactometer have shown that the female Culex quinquefasciatus and Cx.nigripalpus mosquitoes, species responsible for transmitting WNV, are attracted to avian hosts much more strongly than to human hosts. From bioassays of solvent washes from the chicken feet, feathers and skin in an olfactometer, it is evident that one or more chemical compounds function as attractants of these WNV spreading mosquitoes. In this study, we explored the use of sorbents to collect these compounds of interest. Anasorb 747 was able to efficiently trap a wide range of different compounds, from non-polar and moderately polar compounds of high volatility. Various collection times were evaluated as well to determine an optimum. The GC/MS data obtained from this method show mostly methyl esters present in the sample. Preliminary data from direct thermal desorption of chicken feathers allowed the identification of slightly polar compounds of high volatility. Compounds obtained by this method were compared to the ones obtained from trapping on Anasorb 747, followed by solvent elution with carbon disulfide. Aldehydes and ketones were mostly observed from direct thermal desorption of chicken feathers, where methyl esters were mostly observed from sorbent trapping and solvent extraction.